John McEnroe turned 60 this year. Wearing his Mets ballcap in the Player’s Garden as the rain fell in Flushing Meadows, McEnroe said to a 60th-birthday well-wisher: “Don’t rub it in.’’ In fact, 2019 marks a bunch of McEnroe milestones. It’s 40 years since McEnroe won his first U.S. Open. It’s 35 years since his magical 1984 season, when he won Wimbledon, the Open and nearly...